[llvm] [AArch64] Handle inttoptr+add+ptrtoint pattern in lowerConstantPtrAuth (PR #189474)

[Oskar Wirga via llvm-commits]

oskarwirga wrote:

> If we don't need it, I'd rather not set LookThroughIntToPtr to true, I think? (The other change should ensure we don't miscompile.)

I see both sides to this. I lean towards supporting this pattern mainly because the parameter already exists and its trivial to support it but since we don't have default cases leading to this pattern we'd be widening what `lowerConstantPtrAuth` needs to support. 

`inttoptr(add(ptrtoint(@global), offset))` is valid IR but it isn't generated by default so I don't know if this path needs to support it. 

https://github.com/llvm/llvm-project/pull/189474